Formation of Side Ledge and Bottom Ledge

The dynamic behavior (formation/dissolution) of the ledge, depending on the electrolyte overheating temperature, thermal resistance of the lining material, and composite of the cryolite–alumina electrolyte, is studied experimentally using a model installation mimicking the actual conditions of the electrolytic aluminum production. A window that enabled the change of the lining material is mounted into the front wall of the installation case. The ledge formation occurs due to a heat flow formed due to the temperature difference of the electrolyte and electrolyzer walls. The electrolyte cryolite ratio (CR) is varied in a range of 2.1–2.5. The alumina concentration in the electrolyte does not exceed 4.5 wt %. The change in the shape of the working space in the electrolyzer during the electrolysis is determined by the ledge thickness. The active ledge formation in the experimental cell starts upon overheating by 3–4 K. It is shown that a thicker ledge is formed at the same overheating temperature with a decrease in the thermal resistance of the lining material from 16 to 14 m2/W, but a decrease in the thermal resistance in the already formed ledge almost does not affect its thickness. Similarly to the industrial electrolyzer, the ledge profile formed in the experimental cell can be conditionally divided into three zones, notably, bottom ledge, ledge at the metal/electrode interface, and side ledge.